Engine is the power source and also heat of an aircraft. Blades are special parts that are in a large quantity and complex in shape, have high precision criteria, and are difficult to process. They are always the key items in engine manufacturing plants, and are reputed as the “heart of heart.” Aircraft blades are connected to tenon grooves in the blade disc by means of the tenons on the bottom of the blades; therefore, the bottom surface of the tenon groove of the tenons of an aircraft blade is a typical stress-concentrated area. When the engine operates, fatigue cracks may occur and develop on the bottom surface of the tenon groove, resulting in blade looseness, vibration, or unbalance, and thereby causing severely compromised engine safety and reliability, reducing service life, and increasing maintenance cost. Hence, it is of crucial importance to carry out surface peening for the bottom surface of the tenon groove to reduce abrasion and inhibit occurrence and development of fatigue cracks.
Laser shock peening (LSP), which is also referred to as laser shot blasting, is a new material surface strengthening technique. LSP utilizes the mechanical effect of shock wave induced by strong laser to process the material, and has the features of high pressure, high energy, super-rapid and super-high strain rate, etc. Residual compressive stress layer formed by LSP can effectively eliminate stress concentration in the material and inhibit crack occurrence and development, and thereby significantly improve the fatigue life, corrosion resistance, and wear resistance of metal parts. It has been proven through many studies that LSP is an effective means for extending crack occurrence time, reducing crack development speed, and improving material life.
However, the bottom of the tenon groove of the tenon of the aircraft blade is very narrow, usually only several millimeters. During a LSP process, the laser beam irradiates the side wall of the bottom of the tenon groove and produces plasma therein first, creating a “plasma shielding” effect, which hinders the laser beam from irradiating to the bottom surface of the tenon groove and affecting the effect of LSP. In addition, owing to the strong wall-attachment effect of water flow, it is difficult to form a uniform and stable water confinement layer on the bottom of the tenon groove, which also affects the effect of LSP. However, the bottom of the tenon groove is a part that is easy to fail, and surface peening is especially desired.